Highly Ionized Fe-K Absorption Line from Cygnus X-1 in the High/Soft State Observed with Suzaku

Abstract

We present observations of a transient He-like Fe K alpha absorption line in Suzaku observations of the black hole binary Cygnus X-1 on 2011 October 5 near superior conjunction during the high/soft state, which enable us to map the full evolution from the start and the end of the episodic accretion phenomena or dips for the first time. We model the X-ray spectra during the event and trace their evolution. The absorption line is rather weak in the first half of the observation, but instantly deepens for ~10 ks, and weakens thereafter. The overall change in equivalent width is a factor of ~3, peaking at an orbital phase of ~0.08. This is evidence that the companion stellar wind feeding the black hole is clumpy. By analyzing the line with a Voigt profile, it is found to be consistent with a slightly redshifted Fe XXV transition, or possibly a mixture of several species less ionized than Fe XXV. The data may be explained by a clump located at a distance of ~10^(10-12) cm with a density of ~10^((-13)-(-11)) g cm^-3, which accretes onto and/or transits the line-of-sight to the black hole, causing an instant decrease in the observed degree of the ionization and/or an increase in density of the accreting matter. Continued monitoring for individual events with future X-ray calorimeter missions such as ASTRO-H and AXSIO will allow us to map out the accretion environment in detail and how it changes between the various accretion states.

6 pages, 4 figures, ApJL accepted on February 28, 2013

References in corpus (11)

• X-ray Properties of Black-Hole Binaries
• The Mass of the Black Hole in Cygnus X-1
• The Trigonometric Parallax of Cygnus X-1
• The ASTRO-H Mission
• In-Orbit Performance of MAXI Gas Slit Camera (GSC) on ISS
• Superorbital variability of X-ray and radio emission of Cyg X-1 - II. Dependence of the orbital modulation and spectral hardness on the superorbital phase
• Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system. I. The non-dip spectrum in the low/hard state
• Using the X-ray Dust Scattering Halo of Cygnus X-1 to determine distance and dust distributions
• Data-oriented Diagnostics of Pileup Effects on the Suzaku XIS
• Dramatic Variability of X-ray Absorption Lines in the Black Hole Candidate Cygnus X-1
• Improvements in calibration of GSO scintillators in the Suzaku Hard X-ray Detector

Cited by in corpus (10)

• WATCHDOG: A Comprehensive All-Sky Database of Galactic Black Hole X-ray Binaries
• Confirmation Via the Continuum-Fitting Method that the Spin of the Black Hole in Cygnus X-1 is Extreme
• The Reflection Component from Cygnus X-1 in the Soft State Measured by NuSTAR and Suzaku
• Long term variability of Cygnus X-1: VII. Orbital variability of the focussed wind in Cyg X-1 / HDE 226868 system
• Warm and thick corona for magnetically supported disk in GBHB
• Color-color diagrams as tools for assessment of the variable absorption in high mass X-ray binaries
• A New Possible Accretion Scenario for Ultra-Luminous X-ray Sources
• XRISM High-Resolution X-ray Spectroscopy of Cygnus X-1 -- highly ionized Iron absorption structures
• Orbital modulations of X-ray light curves of Cyg X-1 in its low/hard and high/soft states
• Semi-Analytical Model for Wind-Fed Black Hole High-Mass X-ray Binaries -- State Transition Triggered by Magnetic Fields from the Companion Star --